Management of allocation for alias devices

ABSTRACT

Embodiments of the present invention provide systems, methods, and computer program products for managing computing devices to handle an input/output (I/O) request. In one embodiment, the I/O request may eligible for performance throttling based, at least in part, on the associated importance level for performing the received I/O request and one or more characteristics of the received I/O request. Embodiments of the present invention provide systems, methods, and computer program products for throttling the I/O request and transmitting the I/O request to a storage controller.

STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINTINVENTOR

The following disclosure(s) are submitted under 35 U.S.C. §102(b)(1)(A):

Disclosure(s)

(1) IBM United States Hardware Announcement 114-171 “IBM DS88790Delivers Resiliency Functions to Support Multiple-Site Disaster Recoveryand Additional Capacity Within the Same Space,” Oct. 6, 2014,http://www-01.ibm.com/common/ssi/ShowDoc.wss?docURL=/common/ssi/rep_ca/1/897/ENUS114-171/index.html&lang=en&request_locale=en.

BACKGROUND OF THE INVENTION

The present invention relates generally to the management of computingdevices, and more particularly to managing alias devices in a computingenvironment to optimize processing of I/O requests.

Data storage devices are used for storing and retrieving digitalinformation. Often input/output (I/O) requests are to be executed by astorage controller to the data storage devices in order to performnecessary read/write operations for a particular process. Typically, ina multi-system environment, a large number of incoming I/O requests canbe processed by base devices, alias devices, and eventually executed bythe storage controller. For example, in System z®, each I/O device isdefined to the I/O configuration and is represented by a sub-channel ina processor and a unit address in the storage controller. When an I/Orequest is issued to a device, only one I/O request can be active on thesub-channel at a time. Therefore, if multiple I/O requests for a devicearrive at the same time, a portion of those I/O requests may be queuedinternally by the operating system and accumulate I/O queuing timedelay. In System z® environments, parallel access volumes (PAVs) may beimplemented to address this queueing time delay. With PAV, one or morealias devices can be configured that are used to perform I/O requests tothe base device, when the sub-channel for the base device is busy withanother I/O request. Alias devices do not represent an actual logicalvolume on the storage controller; rather they simply provide a pathway(i.e., a sub-channel) that allows System z® to do more than one I/Ooperation in parallel to the same base device.

Typically, there are a number of models used to manage PAV aliases. Themost efficient model with regard to performing multiple I/O requests iscalled HyperPAV. Prior to System z® implementing a HyperPAV model, aliasdevices were bound to a particular base device for a period of time andmoved when needed to another base device. However, aliases were movedinfrequently and only after the workload experienced I/O queuing delays.Usually, with a HyperPAV model, alias devices are put into a pool andused only for the duration of an I/O request and then they are put backinto the pool. This allows less alias devices to be defined since theirusage is managed more efficiently.

In one example where a HyperPAV model is implemented, base devices mayexperience delays when performing a large number of queued I/O requests.In this instance, alias devices may be more likely to be selected andassigned to the base devices that are experiencing processing delays,which may result in unwarranted consumption of alias devices in thealias device pool. Accordingly, the consumed alias devices will beunavailable to perform I/O requests for base devices that are notexperiencing processing delays.

For example, for disaster recovery purposes, an Extended Remote Copy(XRC) process may be implemented to copy data asynchronously from alocal site to a remote site. In this instance, the remote site may readdata from a local device in a local site over a long distance link.Furthermore, data may be written to the local device from the local siteat a faster rate than a remote device in the remote site can read fromthe local device over the long distance link. Accordingly, a storagecontroller that controls the local device will inject delays for writerequests that are being issued from the local site. This delay, known asXRC pacing delay, allows the remote site to catch up on performing readrequests for copying data asynchronously.

In another example, a storage controller with a hard disk drive (HDD)may process a write operation of an I/O request. Furthermore, the writeoperation is processed by first copying data to be written to anon-volatile storage (e.g., cache memory within the storage controller)and then eventually de-staging the data to be written to a storagedevice. In this instance, if a large number of write operations, or alarge amount of data for each write operation is generated, then thestorage controller may not be able to synchronously process the writeoperations at the rate in which write operations are being generated,since it is not able to de-stage the data already in non-volatilestorage fast enough. Typically, in this manner, a processing delay mayoccur for write operations, and can affect a process for a subset ofbase and alias devices to perform necessary I/O requests.

In yet another example, a storage controller may limit access to itsresources (memory, CPU, disk drives etc.) based on an I/O requestimportance level. Usually, if there is contention for its resources, thestorage controller may internally delay lower importance I/O requests toallow higher importance I/O requests to get access to those resources.

In yet another example, a storage controller may implement storagetiers, such that data not recently referenced by storage computer systemmay be migrated to slower storage tiers. In this instance, once the datais moved to a slower storage tier, additional time may be required toretrieve the data the next time the data is referenced. For example, thestorage controller may implement a first storage tier which may involvedelaying I/O requests for an amount of time it takes to spin a disk of astorage device (i.e., a platter of a HDD). In another example, thestorage controller may implement a second storage tier which may involvedelaying I/O requests for an amount of time it takes to retrieve datafrom a tape storage device. Accordingly, this delay as a result ofimplementing storage tiers can affect a process for a subset of base andalias devices to perform necessary I/O requests.

SUMMARY

Embodiments of the present invention provide systems, methods, andcomputer program products for managing input/output (I/O) requests in acomputing environment. In one embodiment of the present invention, amethod is provided comprising: receiving, by one or more computerprocessors, an input/output (I/O) request, wherein the received I/Orequest includes an associated importance level for performing thereceived I/O request by a storage controller; responsive to determiningthat a base device is not available to handle the received I/O request,determining, by one or more computer processors, whether the receivedI/O request is eligible for performance throttling based, at least inpart, on the associated importance level for performing the received I/Orequest and one or more characteristics of the received I/O request; andtransmitting, by one or more computer processors, the received I/Orequest to the storage controller with an indication of whether thereceived I/O request is eligible for performance throttling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a computing environment, in accordance withan embodiment of the present invention;

FIG. 2 is a flowchart illustrating operational steps for sending an I/Orequest to a storage controller, in accordance with an embodiment of thepresent invention;

FIG. 3 is a flowchart illustrating operational steps for processing areceived I/O request by a storage controller, in accordance with anembodiment of the present invention;

FIG. 4 is a flowchart illustrating additional operational steps forprocessing a received I/O request, in accordance with an embodiment ofthe present invention; and

FIG. 5 is a block diagram of internal and external components of thecomputer systems of FIG. 1, in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide systems and methods tomanage allocation of a plurality of alias devices to perform I/Orequests in a computing environment. Embodiments of the presentinvention can provide systems and methods to prioritize performing theI/O request based, at least in part, on an importance level for the I/Orequest. Furthermore, embodiments of the present invention may providesystems and methods to manage a processing delay by determining a mannerto allocate one of the plurality of alias devices.

FIG. 1 is a functional block diagram of computing environment 100, inaccordance with an embodiment of the present invention. Computingenvironment 100 includes primary computer system 110 and storagecomputer system 130, interconnected via network 120. Primary computersystem 110 and storage computer system 130 can be desktop computers,laptop computers, specialized computer servers, or any other computersystems known in the art. In certain embodiments, primary computersystem 110 and storage computer system 130 represent computer systemsutilizing clustered computers and components to act as a single pool ofseamless resources when accessed through network 120. For example, suchembodiments may be used in data center, cloud computing, storage areanetwork (SAN), and network attached storage (NAS) applications. Incertain embodiments, primary computer system 110 and storage computersystem 130 represent virtual machines. In general, primary computersystem 110 and storage computer system 130 are representative of anyelectronic devices, or combination of electronic devices, capable ofexecuting machine-readable program instructions, as described in greaterdetail with regard to FIG. 5.

Primary computer system 110 includes one or more base devices 112, aplurality of alias devices 114, and operating system 116. Primarycomputer system 110 may generate input/output (I/O) requests to beperformed by base devices 112 and/or alias devices 114. For example, anoperation of primary computer system 110 may involve moving data fromprimary computer system 110 to one of storage devices 134 in storagecomputer system 130. In this instance, one or more I/O requests areperformed by primary computer system 110 and components therein tofacilitate movement of the data from primary computer system 110 to oneof storage devices 134. In one embodiment, primary computer system 110is configured for multiple logical partitions to share machineresources. Each logical partition runs an instance of operating system116 (e.g., z/OS®, z/VM®, z/Linux etc.). In this instance, if multiplelogical partitions can access the same device (e.g., one of a pluralityof alias devices 114 or one of one or more base devices 112), then eachof the multiple logical partitions has their own sub-channels for therespective devices. Furthermore, operating system 116, such as z/VM®,may support multiple guests (i.e., operating system 116 images) runningon top of it. Furthermore, each guest would have its own virtualsub-channel assigned by z/VM®. Accordingly, there is one sub-channel perdevice, wherein the device may be one of a plurality of alias devices114 or one of one or more base devices 112. In this embodiment, the I/Orequest is performed by primary computer system 110 and componentstherein by executing a read/write operation to one of storage devices134. In this embodiment, only one sub-channel can be active to performan I/O request in primary computer system 110 at a time. Furthermore,there is no restriction regarding a number of sub-channels active toperform an I/O request. For example, if there are two base devices 112and three alias devices 114, then five sub-channels may be active foreach of five operating system 116 images (i.e., an instance of operatingsystem 116 running on a processor of primary computer system 110).Stated differently, each operating system 116 image may only perform oneI/O request at a time to each of its sub-channels. In another example, alarge number of I/O requests for a single device (i.e., one of one ormore base devices 112 or one of the plurality of alias devices 114) maybe required to be performed. In this instance, a processing delay (i.e.,queue time) will occur at the device level if the number of concurrentI/O requests exceed the number of aliases at any point in time.

Each of one or more base devices 112 represents a single logical volumeon storage controller 132 and interacts with operating system 116 andthe plurality of alias devices 114 to perform I/O requests. An I/Orequest may be received for base device 112 that is available to performan I/O request (i.e., an available logical volume). In this instance,the first of base device 112 has an associated sub-channel (i.e.,pathway) to interact with storage controller 132 in order to perform theI/O request. In another example, an I/O request may be performed by afirst of the plurality of alias devices 114, if base device 112 isunavailable to perform the I/O request. In this instance, computingenvironment 100 may utilize a HyperPAV model, wherein the first of theplurality of alias devices 114 is selected from a pool of alias devices114 and assigned to base device 112 that is unavailable to perform theI/O request, such that the first of the plurality of alias devices 114is configured to perform the I/O request. Furthermore, the first of theplurality of alias devices 114 is returned to the pool of alias devices114 after completing the I/O request.

Alias devices 114 are additional devices that are used by operatingsystem 116 to perform I/O requests to base device 112 when base device112 is busy with another I/O operation. In this embodiment, each of theplurality of alias devices 114 is assigned a sub-channel to perform anI/O request. In one embodiment, computing environment 100 may utilize aHyperPAV model to perform a number of I/O requests in parallel andreduce a potential processing delay resulting from a large number ofqueued I/O requests. Furthermore, the HyperPAV model is implemented toservice a workload (i.e., performing a number of I/O requests) moreeffectively (i.e., using a lesser number of alias devices) compared toother parallel access volume (PAV) models. For example, another PAVprocess (i.e., static PAV) may rigidly assign a first of a plurality ofalias devices 114 to base device 112, regardless of whether base device112 is available to perform an I/O request. In this instance, aparticular workload may have a longer processing delay and use a greaternumber of alias devices 114 when computing environment 100 implements astatic PAV model compared to a HyperPAV model.

Operating system 116 is software that manages primary computer system110 hardware, software resources of primary computer system 110, andprovides common services for primary computer system 110 programs. Inanother embodiment, storage computer system 130 may be a part of primarycomputer system 110, in which case, operating system 116 also managesstorage computer system 130 hardware, software resources of storagecomputer system 130, and provides common services for storage computersystem 130 programs. In this embodiment, operating system 116 managesone or more devices of the primary computer system 110 (e.g.,determining if one of base devices 112 is available to perform an I/Orequest, managing selection and assignment of each of the plurality ofalias devices 114 in the pool of alias devices 114, etc.), andprocessing of I/O requests (e.g., queueing I/O requests, determinationof importance levels for I/O requests, throttling I/O requests, startingI/O requests etc.).

Network 120 can be, for example, a local area network (LAN), a wide areanetwork (WAN) such as the Internet, or a combination of the two, andinclude wired, wireless, or fiber optic connections. In general, network120 can be any combination of connections and protocols that willsupport communications between primary computer system 110 and storagecomputer system 130, in accordance with a desired embodiment of theinvention.

Storage computer system 130 is secondary computer system containingstorage controller 132. In this embodiment, storage computer system 130is a separate computer system from primary computer system 110 and isconfigured to contain one or more storage devices 134 managed by storagecontroller 132. In another embodiment, storage computer system 130 andcomponents therein may be disposed within primary computer system 110.

It should be understood that, for illustrative purposes, FIG. 1 does notshow other computer systems and elements which may be present whenimplementing embodiments of the present invention. For example, whileFIG. 1 shows a single primary computer system 110 and a storage computersystem 130, computing environment 100 can also include more than oneprimary computer system 110 and storage computer system 130.Furthermore, words such as “first” and “second” are used herein forconvenience of description and do not imply any specific ordering.

FIG. 2 is a flowchart 200 illustrating operational steps for sending anI/O request to storage controller 132, in accordance with an embodimentof the present invention. In this embodiment, operating system 116performs operational steps described herein. Furthermore, the I/Orequest performed by primary computer system 110 and components thereinhas an associated importance level. The phrase, “importance level,” asused herein, indicates a priority for performing the I/O request. Forexample, an I/O request having a high importance level (e.g., animportance level of 1 or 2) is handled differently compared to an I/Orequest having a medium importance level (e.g., an importance level of 3or 4) or having a low importance level (e.g., an importance level of 5).In this embodiment, throttling an I/O request involves delaying aprocess to perform the I/O request in accordance with a condition (e.g.,importance level of the I/O request, etc.). It should be understood thatin this embodiment an importance level of 5 is less important than animportance level of 4, 3, 2, and 1 for an I/O request. Furthermore, inthis embodiment, five importance levels are implemented to categorize anI/O request. In other embodiments, a lesser or greater number ofimportance levels may be implemented, as well as other numbering models,and/or other methods to categorize an I/O request.

In step 202, operating system 116 receives an I/O request. In thisembodiment, operating system 116 receives the I/O request from anapplication of primary computer system 110. Furthermore, the applicationof primary computer system 110 may submit one or more I/O requests,wherein each of the one or more I/O requests is to be performed by basedevice 112 or one of a plurality of alias devices 114. For example, theapplication can generate application data to be written in one or morestorage devices 134, or the application can read the application datastored in the one or more storage devices 134. In this instance, the oneor more I/O requests submitted by the application may correspond to oneor more read/write operations to be executed to the one or more storagedevices 134. Furthermore, an importance level for the received I/Orequests may be determined or assigned by operating system 116. Inanother embodiment, operating system 116 may recognize whether an I/Orequest that is submitted is an initial I/O request or an I/O requestresubmitted responsive to an error recovery process (ERP). For example,performing an I/O request may result in an I/O request error, and insome instances, after analyzing the I/O request error operating system116 may retry processing the I/O request. Furthermore, the I/O requestthat resulted in the I/O request error may have been previously rejectedby storage controller 132 because storage controller 132 determined thatperforming the I/O request would exceed a processing delay threshold. Inthis instance, operating system 116 retries the I/O request, such thatthe I/O request is not rejected once again.

In step 204, operating system 116 determines whether base device 112 isbusy. In this embodiment, operating system 116 determines whether basedevice 112 is busy (i.e., unavailable to perform the received I/Orequest) based, at least in part, on whether base device 112 isperforming another I/O request received at an earlier time.

If in step 204 operating system 116 determines that base device 112 isnot busy, then in step 206, operating system 116 uses base device 112 tosend the received I/O request to storage controller 132. In oneembodiment, the received I/O request may be sent to storage controller132 with an I/O delay tolerance flag, as further described in step 214.In another embodiment, the received I/O request may be sent to storagecontroller 132 with an I/O delay tolerance flag for base device 112.Furthermore, storage controller 132 may execute the received I/O requestto one or more storage devices 134, responsive to storage controller 134determining that executing the received I/O request does not exceed aprocessing delay threshold. In another instance, storage controller 132may reject the received I/O request and return status associated withthe received I/O request, then operating system 116 may re-queue (i.e.,throttle) the received I/O request if base device 112 or a first of aplurality of alias devices 114 is not available in accordance to athrottling scope. Furthermore, the processing delay threshold isdetermined by storage controller 132 and may vary based on importancelevel (e.g., higher importance I/O requests may have higher processingdelay thresholds than lower importance I/O requests). Operational stepsfor a manner in which storage controller 132 processes a received I/Orequest are described in greater detail later in this specification withregard to FIG. 3.

If in step 204 operating system 116 determines that base device 112 isbusy, then in step 208, operating system 116 determines whether one ofthe plurality of alias devices 114 is available to perform the receivedI/O request. In this embodiment, the first of the plurality of aliasdevices 114 is available if the first of the plurality of alias devices114 can be selected and assigned to base device 112 that is busy, suchthat the first of the plurality of alias devices 114 can perform thereceived I/O request.

If in step 208 operating system 116 determines that the first of theplurality of alias devices 114 is not available to perform the receivedI/O request, then in step 220, operating system 116 leaves the receivedI/O request queued for subsequent processing. In one embodiment, if instep 218 operating system 116 determines that a usage condition for thepool of alias devices 114 is not met, then in step 220, operating system116 leaves the received I/O request queued for subsequent processing.For example, operating system 116 may perform the I/O request at a latertime when base device 112 or the first of the plurality of alias devices114 becomes available.

If in step 208 operating system 116 determines that the first of theplurality of alias devices 114 is available to perform the received I/Orequest, then in step 210, operating system 116 determines whether thereceived I/O request match conditions for throttling. In one embodiment,operating system 116 determines whether the characteristics of thereceived I/O request match the conditions for throttling (based onimportance level, type of I/O operation etc.). In one embodiment,operating system 116 determines whether the received I/O request isbeing throttled based on feedback indication previously provided bystorage controller 132, as described in greater detail later in thisspecification with regard to FIG. 3.

If in step 210 operating system 116 determines that the type of thereceived I/O request is being throttled, then in step 218, operatingsystem 116 determines whether a usage condition for the pool of aliasdevices 114 is met. In this embodiment, the usage condition isimplemented to determine whether to allocate a first of the plurality ofalias devices 114 from the pool of alias devices 114.

The usage condition may involve determining the type (e.g., importancelevel) of the received I/O request, and determining a percentage ofavailable alias devices 114 from the pool of alias devices 114. Forexample, the usage condition for allocating the first of the pluralityof alias devices 114 to perform an I/O request may include: if animportance level for the I/O request is 1 and 90% or less of aliasdevices 114 in the pool of alias devices 114 are in use; if animportance level for the I/O request is 2 and 80% or less of aliasdevices 114 in the pool of alias devices 114 are in use; if animportance level for the I/O request is 3 and 70% or less of aliasdevices 114 in the pool of alias devices 114 are in use; if animportance level for the I/O request is 4 and 60% or less of aliasdevices 114 in the pool of alias devices 114 are in use; and if animportance level for the I/O request is 5 and 50% or less of aliasdevices 114 in the pool of alias devices 114 are in use. In anotherembodiment, the usage condition may be variable depending on whether oneor more particular importance levels for I/O requests are missing,meeting, or exceeding their respective performance goals.

The usage condition may also be based on another characteristic of theI/O request (i.e., a scope). In this instance, the usage condition mayallocate a first of the plurality of alias devices 114 to perform onlyI/O requests that perform read operations, or I/O requests that performwrite operations, or I/O operations that have other characteristics suchas the amount of data written or read, or whether a certain feature isused in the I/O request. In this instance, the usage condition mayindicate that a write I/O request having an importance level of 3 orgreater must be throttled (i.e., not to be performed until theconditions that caused the throttling no longer exist). In this manner,the write I/O request may not be assigned to a first of the plurality ofalias devices 114, if 71 or more alias devices 114 the pool of aliasdevices 114 are in use. Furthermore, since the usage condition did notspecify throttling of read I/O requests, a read I/O request associatedwith any importance level is not subject to the alias usage condition.It should be understood that either storage controller 132 signalsoperating system 116 that the usage condition for the processing delayin storage controller 132 no longer exists, or operating system 116 maydetermine to end throttling after a period of time.

If in step 210 operating system 116 determines that the type of thereceived I/O request is not being throttled, then in step 212, operatingsystem 116 determines whether the received I/O request is a new request.For example, as previously discussed, an application of primary computersystem 110 may resubmit an I/O request, responsive to performing an ERP.In this instance, operating system 116 may determine that theresubmitted I/O request is not a new request.

If in step 212 operating system 116 determines that the received I/Orequest is a new I/O request, then in step 214, operating system 116sets an I/O processing delay tolerance flag associated with the receivedI/O request. In this embodiment, the I/O processing delay tolerance flagis set to be associated with the received I/O request, such that, whenthe received I/O request is sent to storage controller 132 (step 206),storage controller 132 is configured to perform operational steps asdescribed in greater detail later in this specification with regard toFIG. 3.

If in step 212 operating system 116 determines that the received I/Orequest is not a new I/O request, then in step 216, operating system 116selects a first of the plurality of alias devices 114 to assign to basedevice 112 to perform the received I/O request. Furthermore, operatingsystem 116 may assign a first of the plurality of alias devices 112 tobase device 112 to perform the received I/O request responsive tosetting an I/O request processing delay threshold associated with thereceived I/O request, as previously described in step 214. A HyperPAVmodel may be implemented by computing environment 100, such that thefirst of the plurality of available alias devices 114 is selected from apool of alias devices 114 and assigned to base device 112. Accordingly,once the first of the plurality of available alias devices 114 completesperforming the received I/O request, the first of the plurality of aliasdevices 114 is returned to the pool of alias devices 114, as previouslydiscussed.

If in step 218 operating system 116 determines that the usage conditionfor the pool of alias devices 114 is met, then in step 216, operatingsystem 116 selects a first of the plurality of available alias devices114 to assign to base device 112 to perform the received I/O request.

FIG. 3 is a flowchart 300 illustrating operational steps for processinga received I/O request, in accordance with an embodiment of the presentinvention. In one embodiment, storage controller 132 may determinewhether to reject a received I/O request if the received I/O request isassociated with a set I/O processing delay tolerance flag, as previouslydescribed in step 214 of FIG. 2.

In step 302, storage controller 132 receives an I/O request fromoperating system 116, as previously discussed in greater detail withregard to step 206 of FIG. 2.

In step 304, storage controller 132 determines whether an I/O processingdelay tolerance flag is set for a received I/O request. In oneembodiment, the I/O processing delay tolerance flag is set by operatingsystem 116, as previously described in step 214 of FIG. 2.

If in step 304, storage controller 132 determines that the I/Oprocessing delay tolerance flag is not set for the received I/O request,then in step 310, storage controller 132 processes the I/O request. Inthis embodiment, storage controller 132 starts the I/O request byexecuting a read/write operation for the I/O request to one or morestorage devices 134. In one embodiment, storage controller 132 processesthe I/O request subsequent to determining that performing the I/Orequest will not exceed the processing delay threshold (step 306, “no”branch).

If in step 304, storage controller 132 determines that the I/Oprocessing delay tolerance flag is set for the received I/O request,then in step 306, storage controller 132 determines whether performingan I/O request will exceed a processing delay threshold. For example,storage controller 132 may determine a processing delay threshold basedon a condition, such as, how long it takes to de-stage data fromcomponents of one or more storage devices 134 (e.g., a cache to a HDDplatter) to execute a write operation. In another example, a processingdelay threshold may vary based on an importance level for a received I/Orequest. For example, the processing delay threshold may be implementedto avoid unnecessarily consuming a critical resource (i.e., a first ofthe plurality of alias devices 114) that may be used to perform anotherI/O request with a higher importance level. For example, storagecontroller 132 may process one or more I/O requests having a varyingimportance level (e.g., one I/O request having an importance level of 1and another I/O request having an importance level of 5). In thisinstance, storage controller 132 may reject I/O requests with a lowimportance level, but not reject I/O requests with a high importancelevel, to prevent the low importance level from consuming one of theplurality of alias devices 114 from the alias device 114 pool.

If in step 306 storage controller 132 determines that performing the I/Orequest will exceed the processing delay threshold, then in step 308,storage controller 132 updates an I/O status for the I/O requestindicating that storage controller 132 rejects (i.e., throttles) thereceived I/O request. In one embodiment, the status may indicate areason for the rejection. Furthermore, characteristics of the I/Orequest that caused it to be rejected (i.e., a scope of rejection) arealso indicated in the appropriate status in an instance where acondition is met or exceeded by an I/O processing delay.

In step 312, storage computer system 132 returns an I/O completionstatus for the I/O request to operating system 116. In one embodiment,the I/O completion status for the I/O request includes the reason forstorage controller 132 rejecting the I/O request. In another embodiment,the I/O completion status may indicate that the I/O request wasprocessed successfully by storage controller 132.

FIG. 4 is a flowchart 400 illustrating operational steps for processinga received I/O request. In this embodiment, operating system 116receives an I/O completion status for a received I/O request and the I/Orequest from storage controller 132, as previously described in step 312of FIG. 3.

In step 402, operating system 116 determines whether a completion I/Ostatus for a received I/O request indicates that a processing delaytolerance was exceeded. In this embodiment, the completion I/O status isupdated with information indicating whether the processing delaytolerance was exceeded, as previously described in greater detail withregard to step 308 of FIG. 3. Furthermore, operating system 116 examinesthe completion I/O status to determine whether a processing delaytolerance was exceeded when storage controller 132 began processing theI/O request.

If in step 402 operating system 116 determines that the completion I/Ostatus for the received I/O request indicates that the processing delaytolerance was exceeded, then in step 404, operating system 116 savesadditional throttling information for base devices 112 associated withthe rejected I/O request. Furthermore, operating system 116 may flag acontrol block representing base device 112, to indicate that throttlingis in effect. For example, the throttling information may describe ascope of the rejection, including: importance levels of I/O requests,which types of I/O requests (e.g., read operations, write operations,etc.), sizes of I/O requests, etc. It should be noted that, if a scopeof rejection or additional throttling information is not necessarilyspecific to a single base device 112 (e.g., the condition affects alldevices having certain characteristics or belonging to some type oflogical group), a plurality of base devices 112 may be flagged, or othercontrol blocks may be updated.

If in step 402 operating system 116 determines that the completion I/Ostatus for the received I/O request indicates that the processing delaytolerance was not exceeded, then in step 406, operating system 116completes processing of the I/O request.

Operating system 116 may determine that throttling is no longer ineffect for a particular importance level of an I/O request. For example,operating system 116 may test whether throttling is still in effect byperiodically flagging an I/O request as eligible for throttling. In oneembodiment, this may be accomplished by checking whether storagecontroller 132 rejects the I/O request that has been indicated aseligible for throttling. In another example, storage controller 132 mayprovide feedback indicating that a particular importance level or classof I/O requests is no longer being throttled. In one embodiment, thismay be accomplished by providing a flag in the status information forthe I/O request to indicate whether the particular importance level isbeing throttled. In another example, storage controller 132 may presentunsolicited status for base device 112, such as a unit check with sensedata or an attention interrupt, and a corresponding message that must beread by operating system 116 to determine that throttling is no longerin effect. In yet another example, a response time metric may be used todetermine whether throttling is no longer in effect. In this instance,the response time metric could be an existing response time metric thatalready includes the processing delay threshold, such as a disconnecttime, or a new response time metric representing the amount of time forthe processing delay.

FIG. 5 is a block diagram of internal and external components of acomputer system 500, which is representative the computer systems ofFIG. 1, in accordance with an embodiment of the present invention. Itshould be appreciated that FIG. 5 provides only an illustration of oneimplementation and does not imply any limitations with regard to theenvironments in which different embodiments may be implemented. Ingeneral, the components illustrated in FIG. 5 are representative of anyelectronic device capable of executing machine-readable programinstructions. Examples of computer systems, environments, and/orconfigurations that may be represented by the components illustrated inFIG. 5 include, but are not limited to, personal computer systems,server computer systems, thin clients, thick clients, laptop computersystems, tablet computer systems, cellular telephones (e.g., smartphones), multiprocessor systems, microprocessor-based systems, networkPCs, minicomputer systems, mainframe computer systems, and distributedcloud computing environments that include any of the above systems ordevices.

Computer system 500 includes communications fabric 502, which providesfor communications between one or more processors 504, memory 506,persistent storage 508, communications unit 512, and one or moreinput/output (I/O) interfaces 514. Communications fabric 502 can beimplemented with any architecture designed for passing data and/orcontrol information between processors (such as microprocessors,communications and network processors, etc.), system memory, peripheraldevices, and any other hardware components within a system. For example,communications fabric 502 can be implemented with one or more buses.

Memory 506 and persistent storage 508 are computer-readable storagemedia. In this embodiment, memory 506 includes random access memory(RAM) 516 and cache memory 518. In general, memory 506 can include anysuitable volatile or non-volatile computer-readable storage media.Software is stored in persistent storage 508 for execution and/or accessby one or more of the respective processors 504 via one or more memoriesof memory 506.

Persistent storage 508 may include, for example, a plurality of magnetichard disk drives. Alternatively, or in addition to magnetic hard diskdrives, persistent storage 508 can include one or more solid state harddrives, semiconductor storage devices, read-only memories (ROM),erasable programmable read-only memories (EPROM), flash memories, or anyother computer-readable storage media that is capable of storing programinstructions or digital information.

The media used by persistent storage 508 can also be removable. Forexample, a removable hard drive can be used for persistent storage 508.Other examples include optical and magnetic disks, thumb drives, andsmart cards that are inserted into a drive for transfer onto anothercomputer-readable storage medium that is also part of persistent storage508.

Communications unit 512 provides for communications with other computersystems or devices via a network (e.g., network 120). In this exemplaryembodiment, communications unit 512 includes network adapters orinterfaces such as a TCP/IP adapter cards, wireless Wi-Fi interfacecards, or 3G or 4G wireless interface cards or other wired or wirelesscommunication links. The network can comprise, for example, copperwires, optical fibers, wireless transmission, routers, firewalls,switches, gateway computers and/or edge servers. Software and data usedto practice embodiments of the present invention can be downloadedthrough communications unit 512 (e.g., via the Internet, a local areanetwork or other wide area network). From communications unit 512, thesoftware and data can be loaded onto persistent storage 408.

One or more I/O interfaces 514 allow for input and output of data withother devices that may be connected to computer system 500. For example,I/O interface 514 can provide a connection to one or more externaldevices 520, such as a keyboard, computer mouse, touch screen, virtualkeyboard, touch pad, pointing device, or other human interface devices.External devices 520 can also include portable computer-readable storagemedia such as, for example, thumb drives, portable optical or magneticdisks, and memory cards. I/O interface 514 also connects to display 522.

Display 522 provides a mechanism to display data to a user and can be,for example, a computer monitor. Display 522 can also be an incorporateddisplay and may function as a touch screen, such as a built-in displayof a tablet computer.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The terminology used herein was chosen to best explain the principles ofthe embodiment, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

What is claimed is:
 1. A method comprising: receiving, by the one ormore computer processors, a first input/output (I/O) request, whereinthe first I/O request includes an associated importance level forperforming the first I/O request by a storage controller; responsive todetermining that a base device is not available to handle the first I/Orequest, determining, by the one or more computer processors, whetherthe first I/O request is eligible for performance throttling based, atleast in part, on the associated importance level for performing thefirst I/O request and one or more characteristics of the first I/Orequest; determining, by the one or more computer processors, whetherthe first I/O request is eligible for performance throttling based, atleast in part, on throttling information received from the storagecontroller for a second I/O request that was previously received;transmitting, by the one or more computer processors, the first I/Orequest to the storage controller with an indication of whether thefirst I/O request is eligible for performance throttling; responsive todetermining that the throttling information received from the storagecontroller for the second I/O request indicates that a request type ofthe first I/O request is not being throttled, determining, by the one ormore computer processors, whether the first I/O request is a newrequest; and responsive to determining that the first I/O request is anew request, setting, by the one or more computer processors, a flag forthe first I/O request that indicates that the first I/O request iseligible for performance throttling.
 2. The method of claim 1, furthercomprising: allocating, by the one or more computer processors, one ormore of a plurality of alias devices to the base device based, at leastin part, on the associated importance level and a number of theplurality of alias devices in use.
 3. The method of claim 1, wherein theone or more characteristics of the first I/O request include one or morecharacteristics selected from the group consisting of: types of writeoperations for the first I/O request, and types of read operations forthe first I/O request, or amounts of data involved in one or more writeoperations or read operations for the first I/O request.
 4. The methodof claim 1, further comprising: responsive to transmitting the first I/Orequest, receiving, by the storage controller, the first I/O request andthe indication of whether the first I/O request is eligible forperformance throttling; determining, by the storage controller, whetherperforming the first I/O request would exceed a processing delaythreshold; and responsive to determining that performing the first I/Orequest would exceed the processing delay threshold, updating, by thestorage controller, throttling information for the first I/O request toindicate that the first I/O request has been rejected by the storagecontroller.
 5. The method of claim 1, further comprising: receiving, bythe storage controller, the first I/O request and the indication ofwhether the first I/O request is eligible for performance throttling;determining, by the storage controller, whether performing the first I/Orequest would exceed a processing delay threshold; and responsive todetermining that performing the first I/O request would not exceed theprocessing delay threshold, performing, by the storage controller, thefirst I/O request.
 6. A computer program product comprising: one or morecomputer readable storage media and program instructions stored on theone or more non-transitory computer readable storage media, the programinstructions comprising: program instructions to receive a firstinput/output (I/O) request, wherein the first I/O request includes anassociated importance level for performing the first I/O request by astorage controller; program instructions to, responsive to determiningthat a base device is not available to handle the first I/O request,determine whether the first I/O request is eligible for performancethrottling based, at least in part, on the associated importance levelfor performing the first I/O request and one or more characteristics ofthe first I/O request; program instructions to determine whether thefirst I/O request is eligible for performance throttling based, at leastin part, on throttling information received from the storage controllerfor a second I/O request that was previously received; programinstructions to transmit the first I/O request to the storage controllerwith an indication of whether the first I/O request is eligible forperformance throttling; program instructions to, responsive todetermining that the throttling information received from the storagecontroller for the second I/O request indicates that a request type ofthe first I/O request is not being throttled, determine whether thefirst I/O request is a new request; and program instructions to,responsive to determining that the first I/O request is a new request,set a flag for the first I/O request that indicates that the first I/Orequest is eligible for performance throttling.
 7. The computer programproduct of claim 6, wherein the program instructions stored on the oneor more computer readable storage media further comprise: programinstructions to allocate one or more of a plurality of alias devices tothe base device based, at least in part, on the associated importancelevel and a number of the plurality of alias devices in use.
 8. Thecomputer program product of claim 6, wherein the one or morecharacteristics of the first I/O request include one or morecharacteristics selected from the group consisting of: types of writeoperations for the first I/O request, and types of read operations forthe first I/O request, or amounts of data involved in one or more writeoperations or read operations for the first I/O request.
 9. The computerprogram product of claim 6, wherein the program instructions stored onthe one or more computer readable storage media further comprise:program instructions to receive the first I/O request and the indicationof whether the first I/O request is eligible for performance throttling;program instructions to determine whether performing the first I/Orequest would exceed a processing delay threshold; and programinstructions to, responsive to determining that performing the first I/Orequest would exceed the processing delay threshold, update throttlinginformation for the first I/O request to indicate that the first I/Orequest has been rejected by the storage controller.
 10. The computerprogram product of claim 6, wherein the program instructions stored onthe one or more computer readable storage media further comprise:program instructions to, responsive to transmitting the first I/Orequest, receive the first I/O request and the indication of whether thefirst I/O request is eligible for performance throttling; programinstructions to determine whether performing the first I/O request wouldexceed a processing delay threshold; and program instructions to,responsive to determining that performing the first I/O request wouldnot exceed the processing delay threshold, perform the first I/Orequest.
 11. A computer system comprising: one or more computerprocessors; one or more computer readable storage media; programinstructions stored on the computer readable storage media for executionby at least one of the one or more processors, the program instructionscomprising: program instructions to receive a first input/output (I/O)request, wherein the first I/O request includes an associated importancelevel for performing the first I/O request by a storage controller;program instructions to, responsive to determining that a base device isnot available to handle the first I/O request, determine whether thefirst I/O request is eligible for performance throttling based, at leastin part, on the associated importance level for performing the first I/Orequest and one or more characteristics of the first I/O request;program instructions to determine whether the first I/O request iseligible for performance throttling based, at least in part, onthrottling information received from the storage controller for a secondI/O request that was previously received; program instructions totransmit the first I/O request to the storage controller with anindication of whether the first I/O request is eligible for performancethrottling; program instructions to, responsive to determining that thethrottling information first from the storage controller for the secondI/O request indicates that a request type of the first I/O request isnot being throttled, determine whether the first I/O request is a newrequest; and program instructions to, responsive to determining that thefirst I/O request is a new request, set a flag for the first I/O requestthat indicates that the first I/O request is eligible for performancethrottling.
 12. The computer system of claim 11, wherein the programinstructions stored on the one or more computer readable storage mediafurther comprise: program instructions to allocate one or more of aplurality of alias devices to the base device based, at least in part,on the associated importance level and a number of the plurality ofalias devices in use.
 13. The computer system of claim 11, wherein theone or more characteristics of the first I/O request include one or morecharacteristics selected from the group consisting of: types of writeoperations for the first I/O request, and types of read operations forthe first I/O request, or amounts of data involved in one or more writeoperations or read operations for the first I/O request.
 14. Thecomputer system of claim 11, wherein the program instructions stored onthe one or more computer readable storage media further comprise:program instructions to, responsive to transmitting the first I/Orequest, receive the first I/O request and the indication of whether thefirst I/O request is eligible for performance throttling; programinstructions to determine whether performing the first I/O request wouldexceed a processing delay threshold; and program instructions to,responsive to determining that performing the first I/O request wouldexceed the processing delay threshold, update throttling information forthe first I/O request to indicate that the first I/O request has beenrejected by the storage controller.